In many RF and microwave systems used in defense, telecommunications, and instrumentation applications it is necessary that the power level of the signal at certain critical points in the system be monitored and carefully controlled. The signal level may affect the desired range of propagation of the signal in free space, or it might affect the nonlinear performance of elements that follow it, such as power amplifiers. Such systems are called leveling detector systems since the RF power or a part of is detected and converted to a proportional dc value and used in some kind of a feedback scheme, often called a Leveling Loop, to achieve the level desired.
To control the signal level in an RF system three basic requirements are often imposed. First, a small or negligible portion of the signal needs to be sampled. Second, the sampled signal is often desired to be sampled as closely as possible from the forward wave. This is called the directionality of sampling scheme. And third, in order to have good broadband performance, the proportionality of the detected dc voltage to the RF signal power level as a function of the RF frequency should be constant.
Any practical leveling detector system is typically a compromise between these three requirements. Most directional couplers are bandwidth limited so it is difficult achieve good multi-octave bandwidth directivity. Also, the detector element usually has a frequency dependent transfer function, due to chip, parasitic element, and balance issues. For these reasons directional detectors spanning multiple octaves or one or more decade of bandwidth are expensive.
The present invention achieves a practical compromise so that practical leveling accuracy and wide bandwidth performance are realized in such a way that the costs are minimized and performance maximized by a combination of hardware and software means.